I installed Win8 just as soon as I got my T7600 about a month ago and I was getting hourly BSODs... Mine were mostly SATA related faults.I personally don't think the fault lies squarely on Dell but with Dell, MS and Intel. You mention that you have lots of other machines that run Win8 out of the box, are any of them dual LGA2011?
I've read many reports of dual socket LGA2011 systems from several manufacturers not working well with latest gen Quadros/GeForce cards, as well as having Win8 compatibility issues.